At present, imaging from an X-ray machine is generally provided in the form of 2D images, and currently available solutions include Computed Tomography (CT), C-arm Perspective Image, etc. However, 2D image information is only image data of a certain angle or a certain section, which cannot reflect the full view information of the imaging portion.
In recent years, techniques of constructing 3D images using 2D projection images come into being, mainly including:
The Computed Tomography, which comprises using parallel or sectional X-rays to perform ray projection measurement from different angles for the section of the object under detection to obtain 360° ray projection data; performing counter-projection calculation on the ray projection data to obtain a reconstructed image of the 2D slice; then piecing together the continuously obtained 2D slice image data to obtain the 3D reconstructed image data of the target, so that tomography scanning can be carried out using CT, and analysis is conducted in the manner of images. However, the parallel or sectional ray mechanism of CT results in a low light field utilization rate of the X-ray tube.
The Cone Beam Computed Tomography (CBCT), which comprises performing ray perspective projection of the object using a cone-shape stereoscopic beam ray source and an array detector, so that the projection data of a plurality of sections of the object under detection can be obtained by only one scanning. The 3D image of the target can be reconstructed by a series of perspective projections from different angles according to respective reconstruction algorithms. Compared to traditional CT planar ray beam, CBCT is advantageous for its high ray utilization rate and being capable of reconstructing the 3D image. Traditional C-arm X-ray machines nearly meet the application requirements of CBCT, so the CBCT technique has been conveniently applied to C-arm X-ray machines. The process of CBCT scanning using a C-arm X-ray machine desires that the X-ray tube of the C-arm at least rotates 180°+2γ around the detection target, wherein γ is the half angle of the X-ray beam of the CBCT, and then 3D reconstruction is carried out by multi-angle 2D projections.
For the algorithm bases of reconstructing a 3D image based on 2D projection image data, please refer to L. A. Feldkamp, L. C. Davis and J. W. Kress. Practical cone-beam algorithm, J. Opt. Soc. Am. A, vol. 1, no. 6, 1984, pp. 612-619. Such an FDK algorithm is a classical appropriate 3D image reconstruction algorithm, which has a simple mathematical form and can be easily carried out, and moreover, in case of a relatively small cone angle, can achieve a good reconstruction effect, so it has been widely used. In order to adapt to practical conditions for measurement of the C-arm, K. Wiesent made corresponding improvements on the FDK algorithm. Please refer to K. Wiesent, K. Barth, N. Navab, et al. Enhanced 3-D reconstruction algorithm for C-Arm systems suitable for interventional procedures. IEEE Trans. Med. Imag., vol. 19, no. 5, 2000, pp. 391-403.
However, said method for reconstructing a 3D image by a C-arm X-ray machine using CBCT has the following problems:
1. The process of CBCT scanning using a C-arm X-ray machine desires that the X-ray tube of the C-arm at least rotates 180°+2γ around the detection target, and the image is obtained in a long time period, so that the target under detection is radiated under the X-ray for a long time, resulting in a low measurement efficiency.
2. CBCT has an uneven spatial light field intensity distribution, because the light field intensity of the center ray beam of the X-ray beam is greater than the light field intensity at other positions, and such inconsistency in light field intensity would lead to variation of gray level of each perspective image, so that the quality of the 3D image reconstructed on this basis would be affected.
No effective solution has been put forward up till now to solve the problem existing in the prior art on long-time radiation of the target under detection under the X-ray during the process of reconstructing a 3D image by CBCT scanning using a C-arm X-ray machine.